The traditional resolver is an electromagnetic sensor, also known as synchronous resolver. It is a rotatable sensor for angle measurement, and it can be used to measure the angular displacement and the angular velocity of the shaft of rotating objects, formed by the stator and rotor. Thereof the stator windings, as primary side of the transformer, receive the exciting voltage, and the excitation frequency is usually 400, 3000 and 5000 HZ and so on. The rotor windings, as secondary side of the transformer, get induced voltage through electromagnetic coupling. Operating principle of the rotary transformer and the general transformer is similar, expect that primary and secondary windings of the general transformer are relatively fixed, so the ratio of the output voltage and input voltage is constant, while primary and secondary windings of the rotary transformer will change its relative position with the angular displacement of the rotor, so magnitude of the output voltage will change with the angular displacement of the rotor. The voltage amplitude of the output windings is in functional relationship of sine or cosine, or a proportional relationship with the rotor angle, or in linear relationship with the rotor angle in a certain scope.
The Chinese patent, CN2565123Y, published a Hall rotary transformer, compromising linear Hall components, a permanent magnet magnetic ring, a hollow shaft rotor, a stator casing, a casing rear cover, a stator core and a Hall integrated circuit PCB. Four linear Hall components are installed in the stator core, staggered 90° electrical angle, and a specific multi-pole permanent magnet magnetic ring is used, with two ball bearings in the middle of the rotor for supporting the stator, and a spring lamination in the front of the stator for connecting. The problems of this program are that (1) a specific multi-pole permanent magnet magnetic ring is needed, with high requirement of the uniformity of the magnetic poles, so it cannot be in common use of motors with different pole pair numbers; (2) within one circle, the unique zero position is different to be decided, so the absolute angular position detection is not convenient; (3) the overall structure and process is so complex that it is difficult for miniaturization.
The Chinese patent, CN200972824Y, published a improved Hall rotary transformer, compromising linear Hall components, a permanent magnet magnetic ring, a hollow shaft rotor, a stator casing, a stator core and a PCB connecting the Hall components, with the permanent magnet magnetic ring being fixed to the hallow shaft. Its significance lies in that the stator core is toroidal, with at least two mounting holes distributed at 90° space angle on the stator core. The Hall components are fixed in the mounting holes to determine the spatial location of the linear Hall components. However, due to installation gap, overall dimensions of the Hall components, and so on, there will be positional deviation of the linear Hall components in the mounting holes on the stator core in the up, down, left, right, front and back, six degree of freedom in the mounting holes. And as the permanent magnet magnetic ring is fixed on the hollow shaft, with positional deviation and vertical deviation and so on, which will cause amplitude error, phase error and function error of the output of the rotary transformer. Besides, the quality and installation of the permanent magnet magnetic ring will be greatly related to errors, so there are big errors in the traditional Hall rotary transformer and the error consistency is also poor.
If there is 0.1 mm radial position deviation in installation, supposing the external diameter of the permanent magnet is 12 mm, the relative position deviation of 0.1 mm relative perimeter is 0.1/π×12)=0.265%, which is almost equal to 1°/360°=0.278%, indicating that there will be 1° error even if there is one single positional deviation in this Hall rotary transformer. So the technical angle error in the Hall rotary transformer in the above program cannot be better than 1°. As another example, the permanent magnet magnetic ring is fixed to the hollow shaft, and if there is a 0.5° vertical deviation, which is equivalent to 12 sin 0.5°=0.1 mm of the radial position deviation, so there will also be 1° degree of error.
The permanent magnet magnetic rings produce magnetic field of three-dimensional space, and the linear Hall components will produce voltage output in the effect of tangential magnetic-field component and radial magnetic-field component. In the Chinese patent, Bulletin No. CN200972824Y, four linear Hall components is used, and voltage output by two linear Hall components distributed in 180° is subtracted to compensate assembly eccentric of the stator and rotor. But as the radial and tangential magnetic-field component cannot be compensated at the same time, the effect of compensation is not good, which is usually mistaken for problems of uniformity of the magnetic poles.
For the reasons above, in fact, the positional deviation of the existing Hall resolver can only reach about 2°-3°, and the error consistency is poor.
The accuracy and accuracy consistency of the existing Hall resolvers are poor, and its accuracy is one order of magnitude lower than the accuracy of the traditional electromagnetic induction rotary transformer, so it can only be used in the applications of very low accuracy.
In addition, although the Switch-type Hall rotation angle encoder is already a mature technology, its accuracy and resolution are also very low, generally only 100 lines, and the accuracy in the Hall resolver in prior art is equivalent to it.